1. Field of the Invention
The present invention relates to an image-forming material and a process for forming images. More particularly, it is concerned with an image-forming material and a process for forming images which will be used to make second originals (intermediate, transparent sheets on which original drawings are duplicated) in the field of designing and drawing.
2. Related Art Statement
There have been known image-forming materials and development processes for the production of second originals to be used in the field of designing and drawing. According to the conventional method, the image-forming material is prepared by providing a roughened plastics film substrate with a photosensitive resin layer capable of forming a positive relief. The thus prepared image-forming material undergoes positive printing of an original and subsequent development, so that a colored positive relief image (as a second original) is formed on the roughened plastics film substrate.
One of such known methods is disclosed in Japanese Patent Laid-open No. 133440/1985. According to this disclosure, a plastics film substrate with a roughened surface (matte surface) formed by sandblasting is coated with a photosensitive resin layer composed of a diacetone-acrylamide-acrylamide copolymer and a water-insoluble o-quinonediazide compound. The thus prepared sensitive material undergoes positive printing of an original and subsequent development with an alkaline aqueous solution for the formation of a positive relief image. Finally, the positive relief image is dyed with a black dye solution to give a colored positive relief image having an optical density of 2.5.
Similar image-forming methods to that mentioned above are also disclosed in Japanese Patent Laid-open Nos. 203449/1986 and 163847/1988, except that the diacetoneacrylamide-acrylamide copolymer is replaced by a polyvinylpyrrolidone polymer (in the former) or a water-soluble polyamide resin (in the latter).
The above-mentioned conventional image-forming processes have an advantage of being capable of forming a colored positive relief image of the original drawing on a roughened plastics film substrate. However, they also have a disadvantage that the step of dyeing a positive relief image in the development process stains the operator's body and clothing and the working environment with the dye solution used in that step. This trouble has been alleviated by the introduction of automatic development process. This poses another problem associated with the maintenance of the automatic developing machine and the disposal of the dye waste liquid discharged from the automatic developing machine. To address this problem, there has been proposed a method for forming a colored positive relief image without using a dye solution in the development process. (See the above-mentioned Japanese Patent Laid-open Nos. 133440/1985, 203449/1986, and 163847/1988.)
This method consists of forming a photosensitive resin layer (containing a dye or pigment as an essential coloring component) on a roughened plastics film substrate, exposing the sensitive material for positive printing of the original, and forming a colored positive relief image by development with an alkaline aqueous solution. This method obviates the use of a dye solution in the development process. A disadvantage of this method is that the photosensitive resin layer have to contain a large amount of coloring component (dye or pigment) so that the resulting relief image has a sufficient density required for second originals in the field of designing and drawing. Increasing the amount of the coloring component greatly lowers the printing sensitivity of the photosensitive resin layer, which has to be compensated for by a large amount of exposure in positive printing of the original. A large amount of exposure, in turn, tends to cause the base fogging of non-image area due to the sticking of a dye or pigment (from the photosensitive resin layer) to the roughened plastics film substrate. The base fogging may be reduced by extending development with an alkaline aqueous solution. However, extended development forms pin-holes in images and drops out thin lines.
To reduce the base fogging and to increase adhesion between the roughened plastics film substrate and the photosensitive resin layer, there was proposed a new idea in the above-mentioned Japanese Patent Laid-open No. 133440/1985. According to this idea, a resin layer is interposed between the roughened plastics film substrate and the photosensitive resin layer, said resin layer being made of phenolic resin, polyester resin, urethane resin, vinylidene chloride-vinyl acetate copolymer, or vinylidene chloride-acrylonitrile copolymer. Unfortunately, the resin layer is not effective enough to lower the base fogging sufficiently. Moreover, the resin layer remains on the roughened plastics film substrate even after development, lowering the receptivity of pencil, aqueous ink, or oil-based ink for retouching, or increasing the light transmission and hence decreasing the surface whiteness. (This is because the resin layer hides the rough surface of the film substrate.) Another disadvantage of the resin layer is that it is irregularly removed when a part of image is erased with an organic solvent (such as methyl ethyl ketone) after image forming. This causes uneven surface reflection, degrading the appearance of the second original.